The present invention relates to an improved racket frame, and more particularly relates to an improved friction and collapse resistant head portion construction of a fiber reinforced plastic racket frame advantageously usable for a tennis racket.
The fiber reinforced plastic tennis racket frame is as one example comprised of a foamed resin core wrapped and covered by a fiber reinforced plastic resin envelope.
The head portion of the racket frame, especially the outer side thereof opposite to the playing face undergoes considerable frictional defacement during long use of the tennis racket. In the case of beginner players, such frictional defacement on the head portion of the racket frame is in general caused by the fact that the players hit the ground of playing courts or nets on the playing court with the head portion of the racket frame by mistake and that the players tend to carelessly lean on the butt end of the grip portion of the racket frame, thereby strongly pressing the head portion against the ground. Whereas, in the case of veteran players, they often try to scoop up balls on the ground using the racket by scraping the ground surface with the head portion of the racket frame. In either cases, the head portion of the racket frame is subjected to repeated frictional damages.
Excessive defacement on the head portion resulted from the above-described repeated frictional damages has significant influence upon the distribution of strength along the oval-shaped portion of the racket frame defining the playing face and the stretch of the strings, especially that of the main or long strings, causes stress concentration upon the defaced head portion which ends in destruction of the racket frame at striking balls. Such defacement on the head portion also leads to enlarged twist of the oval-shaped portion of the racket frame about the long axis of the playing face and this twist greatly hinders ideal provision of repulsive force on the balls to be striken. Poor provision of the repulsive force seriously degrades racket maneuverability and operational accuracy at striking balls.
In the racket construction, neighbouring main or long strings are formed by a single cord which runs parallel to the long axis of the playing face in order to form a main or long string, passes through a hole formed in the head portion, run along the outer periphery of the head portion towards the neighbouring through hole being in tight pressure contact with the outer surface layer of the fiber reinforced plastic envelope, passes through the neighbouring hole and again runs parallel to the long axis of the playing face in order to form the neighbouring main or long string. The above-described portion of the cord in pressure contact with the outer surface layer of the envelope tends to cause collapse of the outer surface layer after long use due to impulsive load repeatedly imposed upon the playing face. The collapse naturally leads to loosening of the strings building up the playing face. Further, in the case of the coreless racket frame, the internal cavity of the racket frame is exposed outside when the envelope is collapsed and this seriously degrades appearance of the racket.
In order to obviate the above-described troubles, it is proposed to couple a separate protector to the head portion of the racket frame. Use of such a protector may somewhat prevent defacement of the racket frame head portion on one hand. However, on the other hand, attachment of such a separate protector increases actual weight of the racket, i.e. the inertia of the racket. Such increased inertia of the racket does not well meet the recently growing demand for light racket which enables speedy tennis. In addition, attachment of such a separate protector is liable to damage beutiful design of the racket frame. Further loose coupling of the protector or loosening in the coupling of the protector after causes generation of noises jar upon the ear at striking balls. This noise trouble may be avoided by firmly coupling the protector to the head portion. But, in actual use, such firmness in the coupling is not coexistent with easiness in the coupling. It should be further noted that use of such a separate protector does no afford any solution to the collapse problem.